Alison DiLaurentis has had five phones throughout the show. She uses her phone, to keep in touch with her friends and family, use the internet and receive A's Messages. Currently, she has an iPhone 6 Plus.
Later in "EscApe From New York", she uses a burner phone in New York which she bought from a convenience store
In "Thrown From The Ride", you see Alison texting Emily with a white iPhone 4S in a white case. She uses that from season 5 to season 6A.
iPhone 6 Plus
In "We've All Got Baggage", you can see Alison reading her text from Uber A on a white/silver iPhone 6 Plus in a pink damask case.