How to Change iPhone between Silent and Vibrate
If you set the phone to not vibrate on ring, but vibrate on silent, then you could swap your ringtone for one that makes no sound.
You'd have to repeat that for each notification type below, if you wanted nothing at all to make a sound.

I made my own, but Google has a lot of results if you search for 'silent ringtone'

The side switch will then swap between silent [on] &amp; vibrate [off]