Hi @Siddharth, welcome to the Baserow community!
You can use API filters for that. You need to use the listing endpoint and you need to add an additional filter query parameter (filter__{field}__{filter}) to filter the rows based on the phone number.
I’m not sure what you the field id of your phone number field, so I’ll add an example where you need to replace YOUR_FIELD_ID with your the field id of your phone number. It will respond with all the rows where the phone number contains 123456789.
You can find your field is in the API docs here REST API documentation // Baserow.