I have heard of the “Global PPH (GPPH)”. What is it? Is the EPO a participating office?

The GPPH is a multilateral framework between national and regional intellectual property offices which bundles bilateral PPH programmes.

No, the EPO is not a participating office of GPPH.

The EPO maintains PPH programmes with the offices listed in FAQ “Which patent offices maintain PPH programmes with the EPO?”. All PPH programmes at the EPO mirror the conditions applicable to the GPPH.