The practicing illusionist - or adventurer who has struggled with phantoms - is wont to sneer in response that naturally these creatures are real, insofar as their effects are real. (This is the famed Tomiss Theorem, of the academician-elector Shofas Tomiss' essential Propaedeutics of Sorcerie.) But furtherly philosophical illusionists are likely to respond that this, in turn, lacks ontological nuance as to the precise status of phantoms and other illusions. An illusion must not be regarded as something unreal in the sense that (say) a computer or good demon must be regarded as something unreal (something outside of the world, not existing in the sense of not interacting with all of its other parts) but at the same time it is not like (say) a stone or a unicorn, one ordinary object enjoying the full franchise of existence alongside all the others. Illusions are that which, if they were to cease being observed, go away. These are perfectly efficacious and "real" as far as it goes, like laws and money, but like laws and money, a phantom needs real social supports to keep going, and illusionists approaching their Doom often make arrangements for the same.
This answers the question every novice apprentice has - or every wicked apprentice assumes - about phantoms, that being whether they have an internal life. A phantom has "real" experiences if those experiences are observed. The more astute of the apprentices reply: "but wait, aren't our own conscious experiences the same way? Don't we have 'an inner life' only by virtue of observing our own experiences, self-reflectively?" Exactly so. And the scholarly consensus of illusionists is that illusions properly "feel" pain, heartbreak, hopes, and (above all) dreams - but that they need to be observed doing so in order to, just like anything else. (The bright and terrible angels, who in their calculations disregard the good and bad accrued to phantoms, err here; but that is because they see through all lies, which is why they care not for aforesaid laws or money either.) Specifically, they must in practice be observed by others. In principle, infinite levels of self-reflective awareness - I observe that I observe that I observe that I... - would suffice, but who can manage that?
(It also follows from this that phantoms have, in most cases, no subconscious. Most of us have pains, hopes, and dreams that we are not aware of, but phantoms who wish to retain a subconscious must arrange to be under the continuous observation of a psychotherapist.)
An illusionist that manages to stably maintain their continuity of consciousness (much less subconsciousness) after becoming a phantom may be regarded as the rough equivalent of the necromancer that continues on as a liche. Any competent illusionist by definition can arrange to summon illusions to observe her, but these also require their own observers. Demons can also be summoned by allied or indebted spellcasters, but these wretched creatures cannot see goodness, and the phantoliche existing only in the eye of these beholders is wont to be swift corrupted. Angels see goodness and badness both, and with what awful intensity! - but not, as noted, illusions.
The preferred set of arrangements for an illusionist expecting to meet his Doom consists of some kind of entailed land or other passive income - bonds, interest collecting in the bank, and other purely financial instruments are often preferred for aesthetic reasons - supporting fawning servants interacting with (and, above all, observing) a network of illlusionists. Often a charitable foundation for the education of bards is involved; these bards act as the literary critics, psychotherapists, dramaturges, and publicists required to ensure that, however indirectly, the phantoliche exists under continuous observation. Another popular option (with similar aesthetic appeal for the profession) is the religious foundation, with the phantoliche presented as a kind of god. Both may hire adventurers, of course, being limited in mobility.
Atheists derive at least two sources of delight from the phantom. The first is that the limited endurance of phantoms disproves any omniscient being, the second is that if minor cults may have sprung around phantoliches, major ones may have as well. What else could explain the desire of the gods for worshipers, or the popular superstition that if they were to cease to be believed in, the gods would fade? That they are acknowledged by angels is a stumbling block to this theory, but perhaps this is an advanced trick - or perhaps the angels, as poppets of these mighty wizards, refuse to acknowledge other illusions for fear of their power being usurped. Many a mystery cult based around evading the tricks of the Grand Illusionists Who Rule the World forms in the undergrad dorms of the illusionists college, before most illusionists become distracted by the ease of worldly achievements - another trap of the these demiurges, say the cults.
Although becoming a phantoliche requires a lot of work, this is ultimately not why most illusionists disdain to do so. To be continuously observed by others even in one's inner life is unbearable to most humans and like mortal folk; for illusionists, who typically entered the profession that others might perceive them as they might prefer, it is an especially horrid fate. The phantoliche is, almost by definition, a primadonna, and probably had a need to be seen even before their proper Doom.