If the arrest was recent
Start with the county jail
In Pennsylvania, someone who was just arrested and not released is held in the COUNTY JAIL, run by the county (Pennsylvania has 67 counties; the facility is often called the 'county prison' or county correctional facility, and Philadelphia runs its own Department of Prisons), not a state prison, so the PA DOC locator will not show a brand-new arrest.
Pennsylvania participates in the national VINE system (Pennsylvania's statewide VINE), a free way to check custody status and register for alerts by phone, email, or text (search at vinelink.com).
Some counties also post an online jail roster or inmate locator (for example, Philadelphia and Allegheny/Pittsburgh).
For a very recent booking or bail information, call the county jail's booking or records line.
County jails (often called 'county prisons') are run by each of Pennsylvania's 67 counties, and some post an online roster or inmate locator (Philadelphia and Allegheny among them). Use the county's roster or Pennsylvania VINE, and call the jail's booking/records line for a recent booking and the bail amount.