Get the whole thing. Already fitted in a frame. Its so much easier and you rule out most proximity sensor issues. I've done mine three times now. First time I bought the digitiser by itself, then couldn't get the old digitiser off the screen and ended up buying a LCD. Fitted it all and proximity sensor used to near all the time. Drove me mental. Second time I bought the ready made in frame. Took me 20 mins and my phone was back on with working proximity.
**Edit**
A little tip too. Be real careful removing the battery, mine was glued down hard, if you force it the battery will bend, cost me a tenner extra for a noob mistake. Keep heat on and lift carefully lol.
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