apple mail client on iphone does not update with exchange

I went through this when I switched from my iPhone 12 to iPhone 14.  Now with iPhone 15 it happened again.  I have Office 365 with Exchange 365.  The Outlook mail client on the iphone updates perfectly with exchange.  The following occurs with the Apple client.  It connects intially to Exchange and will update as new mails arrive for about 3 or 4 minutes.  Then it stops updating and I get messages "connection to server failed".  My old iPhone 14 still connects properly as does my iPad.  I even tried a manual set up where one enters user name and server name (outlook.office365.com) and with that I get a message "cannot verify".  I can't be the only one experiencing this.  My memory from two years ago is that this fixed itself magically.  But that cant be right.  Ideas?????