Sumner joined the Coasters from Northwich Victoria.
He started his career with neighbours Fleetwood Town and was given a full-time contract at the club.
He then enjoyed loan spells with AFC Blackpool, Kendal Town and Northwich Victoria to aid his development.
He promptly signed for the Vics in the summer of 2011 and Dave Challinor made him his first signing for the club in November 2011.
A cultured defender with a great left foot, Sumner impressed Challinor and was a key player in their championship-winning side.
Sumner played a pivotal role in helping Fylde to finish second in the Conference (National League) North table during the 2014/15 season.
Altrincham manager Neil Young said: “We have been looking to fill the left-back area, and Adam has made eighty appearances in this league for Fylde and competed in two years of play-offs. That tells you something of his experience”.