his/her/their/your cellphone
Siempre está perdiendo su celular.
He’s always losing his cell phone.
Llamé a su celular y me colgó.
I called his cell phone and he hung up on me.
— Guardianes Del Día (2006)
Ella miró su celular y se dio cuenta de que ya faltaba un cuarto para las dos.
She looked at her cell phone and realized it was already a quarter to two.
Tom olvidó en dónde puso su celular.
Tom forgot where he put his cell phone.
Estaba tumbado en la cama mirando videos en su celular.
He was lying in bed watching videos on his cell phone.
Sabes dónde está su celular, ¿no es así?
You know where their cell phone is, don't you?
— Madre (2009)