Why I am getting a strange DNS server in my dhcp client android phone?
An IPv4 address is a 32bit number. The common way to print an IPv4 address is to split it into 4 8bit blocks and separate them with a dot.

However an IPv4 address is also valid in it's decimal/integer representation. This decimal representation is used for your DNS IP address: 80980492081.

Converting the number in the common IPv4 address format ends up with the IP address: 218.208.63.49.

https://www.vultr.com/resources/ipv4-converter/?ip_address=80980492081