It is easier if the phone has a headset port. Then you need a Plantronics MDA200, with a 2714-01 dongle. You also need the correct EHS cable for your phone model. I used this setup for several years, on every phone call and every Webex meeting (not with a Marvel, obviously). The hearing aid pairs with the dongle.
You can also connect your computer to the MDA200 at the same time.