I find it strange that my on my ADSL router, my phones can set Static IP and setup whatever DNS I want and upon DNSLeak test, it shows the DNS server I set.

However on another Unifi TM router, no matter what DNS is set on the phone, it will will never be used, instead defaults to TM DNS. Strangely with laptops and PC, it obeys the DNS that is set on these machines, just Mobile devices do not obey.

What's the reasons for this? Does router have DNS priority eg. the phone disobey the static DNS set inti it but chooses to use router's DNS because router says its DNS is superior?! Any such thing?