- Okay, so you already disabled DHCP on your router and enabled it on the Pi-hole dashboard and it is still causing issues for you?
- Do you have, by any chance, another device in your network that could be handing out IP addresses (another DHCP server)?
- Did you restart the smartphone?
You won't have to specify the DNS server manually on the smartphone when you switched to using the Pi-hole DHCP server as it will always correctly give itself as DNS server in the dynamic IP configuration your devices receive.