How much US currency physically exists, and what percentage of US money is only digital (bank ledger entries)?

The total number of Coins and Currency Notes, etc. are as follows:

Source: The Fed - Data

There was approximately $1.63 trillion in circulation as of March 21, 2018, of which $1.59 trillion was in Federal Reserve notes.

Source: How much U.S. currency is in circulation?

You also need to look at the M1 and M2 money supply.

Money Stock and Debt Measures - H.6 Release

Here is a snapshot of the US Money Supply:

Source: United States Money Supply M0 | 1959-2018 | Data | Chart | Calendar