I have warranty of my phone.But the actual warranty is for 24months,but on my phone it’s showing only for one month.

The “actual” warranty on a new iPhone is ONE YEAR; it starts the date the phone was originally sold by Apple or an Apple authorized reseller. You can check your warranty status here→Apple - Support - Check Your Service and Support Coverage

If you purchased AppleCare+ when the phone was purchased new from Apple that will extend the warranty to 2 years, and is renewable after that.

The warranty for an iPhone is 1 year. If it's showing 1 month, you purchased a phone from a third party vendor. The warranty started the day they purchased it and it has been sitting on the shelf for 11 months.

If you purchased AppleCare+ when you got the phone, and chose to pay monthly for it, the expiration date will update with each payment for the next month. If you paid in full at the beginning you need to check with AppleCare+ Support→Find information about your warranty or AppleCare plan - Apple Support

Use the Get Support link at the bottom of the page.