For anyone coming here, the creation of separate 99X users and devices by FOP2 manager can be toggled by modifying /var/www/html/fop2/admin/config.php
$ZULU_COMBINE= true
Won't create 99xx devices, they will be added as an extra channel for the regular xx PJSIP device.
$ZULU_COMBINE = false
Will create both 99xx and xx devices as separate entities (thus, if creating a fop2 user 99xx it will be able to use the webrtc phone in FOP2.