The Toffees captain announced this week that he intends to leave when his contract expires at the end of the season in order to prolong his playing career.
Moyes began the rebuilding process last summer by allowing experienced midfielder Tim Cahill to leave but he knows further and more significant changes are necessary in order to maintain their competitiveness.
However, with less money available to them than most of their rivals the Scot accepts it will be a difficult task, and that consideration is partly behind his decision to delay deciding on whether to extend his own contract when it runs out in June.
"I do think there is a big rebuilding job to go on at Everton," said Moyes.
"With Phil going that is a big piece of the jigsaw which will leave and if we make Europe we are going to have to find a way of bringing in five or six players because of the way your squad is affected.
"We have a few players getting near the end, we have a little bit of an ageing team
"We have not invested an awful lot over the last five or six years so we have to now be looking to see how we do that, how we get the team moving forward and get some younger players in as well as developing our own.
"That is the hard bit. We have a few players in their 30s and we have to start looking to replace them but supporters also want us to continue playing at the top of the league.
"You get the young players in and they might need a bit of time to settle in and be given that period."