Can anybody please tell me how I stop my sleep focus alarm going off on my phone? So it only vibrates on my watch?

This only happens sometimes but I don’t understand why. Sleep focus is turned on on my watch with the sleep focus alarm set, I turn off the sleep focus on my phone and turn off the mirror my phone option.

Now today the sleep focus alarm sounded on my phone. Why is this?

I hate it as it is way too loud and only want my watch to vibrate.