How do I cancel the auto payment for the SIP I have set up on PhonePe?

You can cancel the auto payment for your SIP by, 

Alternatively, if you have set-up your SIP using netbanking/debit card, you can cancel the NACH mandate that enables automatic payments from all the bank accounts that you’ve used to set-up payments for SIPs.

If you have any other queries related to your NACH cancellation, please contact your bank.