Visit the official UIDAI website
Go to the Aadhaar services section
Select the option to verify mobile number or email linked with Aadhaar
Enter your Aadhaar number and the mobile number you want to check
Enter the captcha code
Submit the details
If the mobile number is linked, you will receive an OTP on that number
If no OTP is received, the mobile number is not linked with Aadhaar
You can also visit an Aadhaar Enrolment or Update Center to check and update the mobile number
Carry your Aadhaar card and valid identity proof if required