The issue with clipping under terrain and getting stuck also happens with Mirror Images on occasion— the slight jink to one side as the two clones are created can easily clip you under"water".
Also, Signet of Illusions does not appear to work on clones at all. It’s not just phantasms.
Finally, clones created by dodging (in the Duelist tree) frequently don’t attack your target and often either dissipate instantly or attack other, random targets — usually critters or other nearby enemies.