how to track someone by phone number

A phone number by itself gives you no location. This is the part the "enter a number and see a map" sites never explain: the number is a routing identifier, not a coordinate. Live location lives with the carrier's network and with the phone's own operating system, and both require the account holder or the device owner to authorize sharing.

What the number can legitimately do:

• Carrier family tools — Verizon Smart Family, T-Mobile FamilyWhere, AT&T Secure Family. The line has to be on your account, and the person on it has to be a family member you administer. Location accuracy comes from the carrier network, so expect a few hundred meters, not a driveway.
• Apple Find My — the other person must accept your Family Sharing invitation and enable Share My Location. Without that opt-in, nothing appears.
• Google Maps location sharing — the recipient must accept a share from their own Google account, with a duration they choose.

If you are tracking a phone you own and administer — a teenager's Android, a family PC — that is where a monitoring product legitimately fits. Ultimate Phone Spy covers Android, Windows and Mac with location history, geofencing and message monitoring under one dashboard (plans and pricing), and it is installed visibly on the device rather than run covertly.

Anything else that claims to resolve a bare phone number to a live location is either a data-broker lookup of public records, or a scam collecting a credit card. Reverse-lookup sites will give you a carrier and a rough region at best.