The present is a really bad idea, he can now call her whenever he likes, he has a direct line to her that he pays the bill for and he knows the number for.
I really think you should not have told the girls of the phone or take away and should have stood your ground. If you have even the tiniest suspicion of sexual or other abuse no amount of presents or meals should encourage you or them to be anywhere near him until this is cleared up.
I am afraid this suggests that you cannot say no to him and really need to seek help to make sure he:
is not abusing them (well we know he is neglecting them when in charge of them but is there more)
IS giving you mainatance to support them, how can he afford iphones and take aways and you struggle for food?
I am sorry to say this but he is shitting on you, and them both, from a great height.
My dd got a tablet at 11 and it has caused so many rows between her and her brother. Electronic devices and bribes are not good parenting for such young kids not if they will cause division and allow him any influence in her life. You should have said no and not told them.
Get help, he is going to grind you down with his good cop bad cop routine.
You do not need to tell them all he says or offers, you do not need to allow him access to them if you suspect he is abusing his position in their lives! (And to me playing one off as favourite is an abuse of power).
Please get help, legal, emotional etc and get some assistance with self esteem and assertiveness training, if you can. You are divorced but he is still calling the shots. Getting drink while you can barely afford to eat!
You need to stop him, make him pay to support his own kids, and get to the bottom of the issues before he gets the privilege of eating with his kids and once again showing how shit he is by favoring one over the other.