Thanks for the tips guys. I guess I should have clarified it a bit. As JB pointed out, the smallest may not be readily available, and as Haraldo pointed out, the smallest day geckos might not be Phelsuma. I am looking for a small species of day gecko that typically stays under 4 inches ( I know I said 3 originally but in doing some research I have found that 4 might be more realistic) that I can keep a pair of in a 30X high. A few that I have found online are:
Phelsuma v-nigra v-nigra
Phelsuma pronki
Phelsuma pusilla pusilla
Phelsuma klemmeri
I think the Klemmeri are available, and I think the pusilla is part of the lineata complex you both mentioned. I'm not sure about the others.
The reason I am looking for small is becasue I also have dart frogs and I raise fruit flies for them. I don't want something so big that I can't use Fruit flies as the major part of the diet. I am not opposed to crickets occasionally but I don't want to be dependent on them.