After T322278: MediaWiki core should pass Phan on PHP 8.1 the next step for T319432: Migrate WMF production from PHP 7.4 to PHP 8.1 would be to make also phan voting under php8.1 for the extensions and skins used by wmf wikis.
(In parallel with phan under php7.4, same situation as for core)
phpunit jobs voting was handeld with T316078: Make PHP 8.1 voting on development (master) branch of MW ecosystem (core, extensions, skins, libraries)

From my local tests all repos are passing at the moment.
It seems that mwext-php81-phan-docker is not running under experimental for extension-quibble