i have talked with 6 ncps and already done the festival quest ，but i also can't find the path in Calbridge Stronghold...

It's also necessary that you had the events with Mira and Mirel at the festival of Thremten and that your relationship with them is high enough. Have mirel in party talking 6 npc that should unlock path hot spring

Is it possible to access the hot springs on a phone?

yes

So it turned out mira affection was to low. Not my fault thinking love potions would work differently 😅