Steward is a member of the Portsmouth academy and is currently on loan at Isthmian Premier League side Bognor Regis Town, until January.
The young goalkeeper has made nine appearances so far for the Rocks, with the club sitting ninth in the table.
Cowley admitted that since going to Bognor, a number of sides from the top two tiers have enquired about Steward, wanting to take him permanently.
However, Portsmouth have remained firm and have refused to sell him, with Cowley outlining his plan to have the shot-stopper develop properly, play at least 100 games for Pompey and then sell him for a big amount.
Speaking to The News, Cowley said: “Toby has done very, very well at Bognor – and since he has been there a Premier League and two Championship clubs have enquired about him again.
“They wanted to take him permanently, but it is not our ambition to sell Toby.
“My ambition for all my young players is to develop them, get them in, enjoy them, for at least 100 games, then sell them for a lot of money.”
Steward was on the bench on occasion for Portsmouth’s League One games last season and he signed a two-year deal with Pompey in February this year.
