I rent bikes most weeks so am constantly attaching and removing my Samsung phone holder from a rental bike, with different size handlebars and places to attach the bracket this has become a pain in the neck. Any suggestions on a phone holder that is very easy to attach and remove, or a dedicated GPS device that I can access ridewithgps that is also easy to attach? Currently, I use a Minoura iH-520-STD.
Thanks in advance.

Welcome to the forum. I find the garmin o-ring mounts fairly easy to attach.

Thanks unterhausen. I will look at it.

Ditto, it's a pair of heavy duty rubber bands that can wrap around the stem or h-bar. Garmin provided this mount with a unit.

Thanks.

You should check out quad-lock. It requires a special case on your phone, but I've had nothing but good experiences with it.

Thanks htown_rider.
I bought a Decathlon waterproof case, it it can be attached or removed within a minute with no trouble.

Take a look at the quad lock system. Those use o-rings like the Garmin. They have many options for mounting.

https://www.quadlockcase.com/