There are so many apps to choose from that it can overwhelming. Here are a few that include Thai translations.
5000 English Phrases - This app as a variety of activities for learning a wide range of phrases and short sentences.
6000 English Words - The easy level is good for beginners that are still learning how to read.
AnkiDroid - This is the best spaced repetition app that I've found. It has lots of user created content. The Android version is free.
Duolingo - This is one of the most popular free apps for learning languages.