Learn Survival Tibetan
Although there is currently not a specific Tibetan phrasebooks, Wikivoyage users have collectively created a free Tibetan phrasebook with the goal of making it possible for travelers to "get by" while traveling in areas where Tibetan is spoken.
Wikivoyage phrasebooks are available in many languages and each one varies in depth and detail. Most of the phrasebooks include a pronunciation guide, a general phrase list, information about dates and numbers, a color list, transportation-related phrases, vocabulary for shopping and phrases for eating and drinking. Some are even more in depth, and all are free!