The site or location number you need to add funds to an inmate's phone account is specific to the phone carrier the facility uses, and it is not something that stays constant across providers or facilities.
The fastest way to get it is to call Hoffman Hall directly and ask. The front desk or a counselor can tell you which phone service provider the facility uses and point you toward the right place to add funds. Most facilities use one of a handful of major providers including Securus, ICSolutions, GTL, or Telmate, and each of those has its own website and customer service line where you can set up an account and locate your facility by name or code.
If your inmate has already made a call, the number that appeared on your caller ID when they called is tied to the carrier's system. Calling that number back often connects you to the carrier's automated system where you can add funds directly without needing to know the site code in advance.
You can also search the carrier's website by facility name. Typing Hoffman Hall, Philadelphia into the search field on Securus.net, ICSolutions.com, or GTL's site will pull up the facility and walk you through the deposit process step by step.
Getting funds on the account quickly is worth the few minutes it takes to track down the right provider, because without a balance your inmate cannot make calls regardless of how the phone system is set up on their end.