spend time on or with mobile phone

[tulipflower]

I asked my students to make sentences with 'used to' and one of them said 'I used to spend time with my phone'.
I know the preposition should be 'on' but it still sounds odd to me. How can she convey the intended meaning?

 

[jutfrank]

She probably means one of the following:

I used to spend a lot of time on my phone.
I used to spend too much time on my phone.