Modem Extension Cable

Okay, so I have a standard ADSL modem/router plugged into the phone port. Everything works well.

We are moving our home office two rooms away and I wish to run a much longer cable from the jack to the modem which will reside in the new office. Can someone advise what it is that I need to purchase? Is it as simple as an old school phone extension? If I know what it's called I'll get one! Probably going to need to be 10m

thanks