Spencer Hastings currently uses an iPhone 6 and she keeps it close to talk to her friends. However in the books, she uses a T-Mobile Sidekick and temporarily, a burner phone.
From the beginning of the show to the end of Season 1, Spencer used an HTC HD2 phone, to contact with her friends, family, and, of course, to receive "A's" Messages.
In "For Whom The Bell Tolls," Spencer, Hanna, Emily and Aria uses a burner phone to blackmail Ian with Ali's videos.
From Season 2 to season 5A, Spencer has a HTC HD7. The HTC HD7 is a Windows phone. Spencer uses her phone to contact her family, Toby, Emily, Hanna and Aria; as well as to receive messages from "A". Since the HD7 is a smartphone, Spencer is able to plan out her day, and keep up with the many things she needs to do and accomplish.
In "EscApe From New York", Spencer uses a burner phone to call the police to report Shana's death.
In "How the 'A' Stole Christmas", Spencer is seen texting Hanna on her black iPhone 5 in a black damask case. When Spencer goes to London, she gets her flat mate to help her use Data Roaming so she can call Aria, Hanna and Emily. Spencer uses this phone a lot during 5B. With this being a smartphone Spencer can pretty much plan out her day, and keep up with the many things she needs to do and accomplish, like with her HTC HD7.
In "The Melody Lingers On", Spencer texts Varjak on the white burner phone, that she borrowed from Caleb.
In Season 6B and onwards, Spencer has a black iPhone 6 in a brown leather case by Tendlin.
Along with Emily, Spencer has an Apple Watch seen in the 6B part of Season 6.
In "How the 'A' Stole Christmas", Spencer's iPhone had iOS8 running on it, but in later episodes it had iOS6.