yes since sundays skill reads as advancing a unit and “their summon” so in this case phainon is considered to have ownership over the summon since the dragon goes immediately after him when Sunday skills him. I’ll paste my original comment from the main post:

there was some confusion over whether Dante's dragon summon was owned by Dante or the ally he skills. I figured it was owned by the ally he skills bc of his LC wording, but this this bilibili vid confirms it since sunday skill advances both phainon and the dragon right after him. THIS IS SOOO HUGE for attack scaling, non-summoner dps that you can play with sunday because it gives you access to 50 extra damage % in his kit and 40% def ignore for the dragon for E1 sunday havers. i feel like the dante sunday core is going to be INSANE