I've been asked to package clementine for EPEL8, as such I need this dependency in EPEL8. Thanks.
phonon currently is in epel8-playground, with the rest of KDE. We plan on KDE in epel8 to be fully released only as a module. This is because we will have to override the QT5 that is released with RHEL8, among other reasons. Modules in EPEL8 are not expected to be ready until sometime in December 2019. For the time being, I suggest trying to build it in epel8-playground, just to make sure you have everything there. Are you sure phonon is what you need? I don't see it as a requirement for clementine, either for building or running.
This bug appears to have been reported against 'rawhide' during the Fedora 32 development cycle. Changing version to 32.
phonon-qt5 is in EPEL8 now. (not just playground)