Alexander is yet to taste defeat with two wins and three draws in five games, including four clean sheets, since he took charge following the sacking of Micky Mellon.
First-half goals by David Ball and Alan Goodall clinched The Cod Army's latest success, with Vale winger Jennison Myrie-Williams seeing his second-half penalty saved by 'keeper Scott Davies.
Alexander said: "I feel we are improving and the boys have done exceptionally well here against a very, very good team.
"To keep a clean sheet and score two goals against a team who were top of the table shows we have done a lot of things right. I was very pleased with all of our players.
"Some of the football we played in the middle and front third of the pitch was exceptional. Vale had chances, but we could also have scored a few more goals.
"We were bound to come under pressure in the second half, but the boys back there did well and we always carried a real threat in our counter-attacks.
"Alex Titchiner was a real livewire and deserved a goal. He and David Ball caused Vale a lot of problems."
Both of Fleetwood's goals came from set-plays, and Alexander added: "They are a massive part of the game and we do a lot of work on them, both attacking and defending."