My experience is that I had to learn every word twice: once as text and again as audio.
This was despite the fact that Brazilian Portuguese is much more regular than English in mapping sounds to letters.
Quizlet and similar ideas look fine for written vocabulary, and helping you read, but don't kid yourself: you're not going to be able to listen and speak by mastering this tool.
Although, to be fair, Brazilian dialects too vary a lot in terms of pronunciation.
We did consider using text-to-speech to say the word out loud once you answer it, but it wouldn't be ideal to have to hear every time you wanted to unlock your phone.
What I mean is, in an absolutely personal opinion/experience:
I still have big troubles understanding spoken hungarian in contrast to written, although pronunciation matches written almost 1:1 I just can't tell the difference between ü u ú Ű) etc.. but at least I can sort of express myself, even if I do it by mispronouncing most words.
So, written does not imply spoken, but it does help.
Although making sentences relevant to the learner is also a big part of language learning, and the FB part does help there. It's almost killing two birds with one stone.