how to hold caller few seconds

There is something odd about your phone's software. Android allows you to switch apps during a call, and always has.

I usually put the call on speaker, just because I won't be holding it to my face while doing this, then just switch apps. No special trick.

 

yeah just like @Hadron said, just put them on speaker.....or you can put the phone on mute while you open up another app.