how i can increase the length of call history in my phone

You cannot. The Recent Calls section will only store the last 100 calls. It is not date dependent. If you would like to see a change in features, then you would need to leave feedback to Apple HERE, and click on the appropriate subject area/

Many wireless providers offer an extended call log via their website.

Perhaps the one you use can provide you the information you wish.

But the iPhone has the limit as ChrisJ4203 discussed above.