How do I tell my phone that I want to send traffic to server A via isp1 and server B via isp2

On your router?

edit Less flippantly, what are you wanting to base the routing rule on? What's your ipv4 routing rule?

DSCP is allowed in ipv6.

	▲	hdgvhicv 2 hours ago \| parent [-]
		Without nat, my understanding is the right way in v6 is to issue addresses of every network and then send a message to each end device asking it to use a specific ip address to route traffic and hope every client implements RFC 4191 in the right way.