in/on silent mode

I would use "in silent mode", or "on silent".

Many thanks, Contrex.

I would say, "my phone is on silent mode".

I think here it depends on what you are focusing on/thinking of, Ms Tan.

My phone is in/on silent mode

because I have set my phone on silent mode.

My phone is in silent mode,

describes its state. I sometimes set my computer in sleep mode.

Many thanks, Canodonald and JTT.