I can also report this behavior both with an iPhone 13 Mini and an
iPhone 16 Pro running iOS 18.2. Perhaps this is something specific to
the interaction of Voiceover and Repeaterphone/CallKit in iOS 18.1 and
newer? Not sure.
I can usually make Voiceover speak through the normal profile again by
switching to another app, initiating then dismissing Siri, then switch
back to Repeaterphone without
the app. Bit of a pain, though.