who is very clever?is it phineas hoặc ferb?

BOTH!!!!

i think phineas because he is always thinks an idea what they do that day.

Both of them are clever but if I had to pick, it is Ferb. I say him because he is the one which always builds the contraptions/inventions of him and his stepbrother.

both

phineas

i agree both phineas and ferb