Safari on the iPhone has a maximum of 500 active tabs
set by Apple. Consider yourself fortunate if you were unaware of this. It indicates you're probably only using a few tabs, which makes things easier for you. However, if you're approaching or have already surpassed that limit (which isn't ideal), you're in desperate need of assistance.
Once you've opened 500 tabs in Safari, iOS won't let you open anymore.
I hope this answer would help you