For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Simmphonie/openSUSE_Tumbleweed/home:Simmphonie.repo
zypper refresh
zypper install libopencore-amrnb0
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Simmphonie/15.5/home:Simmphonie.repo
zypper refresh
zypper install libopencore-amrnb0
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Simmphonie/15.4/home:Simmphonie.repo
zypper refresh
zypper install libopencore-amrnb0