why is the "flag" option no longer on my ipad, iphone?

Hello,

You can access the Flag option a few different ways:

In the bottom right of each Mail message > Tap the curved arrow button > Mark > Flag.

Within the list of message > Long-press the message > Mark > Flag.

Hello,

In iOS 13 the Flag option was moved in Mail, iPhone 6 does not support iOS 13. You can find the flag option by pressing the reply button on the Mail message > Flag.