Portia takes as long to rotate on its axis as it does to make one orbit of Uranus; and therefore always keeps the same hemisphere pointed to Uranus.
The Portian orbit, which lies inside Uranus' synchronous orbital radius, is slowly decaying due to tidal deceleration. The moon will one day either break up into a planetary ring or hit Uranus.
Portia heads a group of satellites called the Portia Group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda and Perdita. These satellites have similar orbits and photometric properties.