I just did yum upgrade on my FreePBX system and took it to 15.0.23. As soon as I did that, I got the following error:
retrieve_conf failed to sym link: /etc/asterisk/res_digium_phone.conf from digium_phones/etc (Already exists, not a link) This can result in FATAL failures to your PBX. If the target file exists and not identical, the symlink will not occur and you should rename the target file to allow the automatic sym link to occur and remove this error, unless this is an intentional customization.
I moved the file to /etc/asterisk/res_digium_phone.conf.bak and that cleared the error. But as soon as I made some changes and applied the changes, the error popped back up.