Really it comes down to the version of Asterisk you are using, you don’t actually need to install the module via yum, digium/sangoma have updated it for various versions of Asterisk as well. If you have Asterisk 13 (which I believe FreePBX 13 supports), you could manually install the latest DPMA for Asterisk 13 which appears to have been updated (today?).
https://downloads.digium.com/pub/telephony/res_digium_phone/asterisk-13.0/
https://wiki.asterisk.org/wiki/display/DIGIUM/DPMA+Installation
But yeah I agree that you should look at updating. Also - make sure the phones have the latest firmware installed, I had issues with a couple that wouldnt connect and a firmware update fixed them.