KardiaMobile does not "pair" to a particular phone or tablet, so if you would like to use it with a different compatible phone all you need to do is install the Kardia app and use it with KardiaMobile.
You may be using the optional phone clip device which is a small, flat, black, slide in case that may have come with your KardiaMobile. If so, you do have the ability to move the Kardia Mobile monitor to a different phone. You simply need to slide the Kardia Mobile out of the phone clip by pressing on the electrodes, and sliding it out of the clip. You can then purchase a new phone clip, and attach it to a new phone case, then simply slide the device into the new phone and phone clip.