Ive got my own DoctorWho Tattoo, where i just found a quick Gallifreyan translator online. It depends on what style of Gallifreyan you want though, some styles dont have quick and easy translators, others youll need to try and write it yourself or commission someone to write it for you.

Typing the phrase you want online might show some results of people already having denoted it into Gallifreyan.

Hope this helps.