Yes you can fly with PH. I have a portable Oxygen Concentrator that I take with me. You do have to contact the airline several weeks in advance to make sure if there is any paperwork needed or if you need extra batteries for long trips.

There is a special test offered at many teaching hospitals that can measure your predicted level of hypoxia at different levels of altitude with air compression and for over various periods of time. Some hospitals call it a Hypoxia Challenge though I forget the term used locally here in Arizona. It’s offered here at both the Mayo in Scottsdale as well as newly at John C Lincoln in Phoenix.

@A myPHteam Member Not all PH patients can fly, with or without O2 assist available to them. Flying offers some conditions that can be untenable for many.

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A myPHtea...

I found an Ai summary of the testing I was talking about. Where I live they call it the High Altitude Simulation Test (HAST).:

The test used to measure predicted hypoxia levels during air travel is commonly called the
hypoxic challenge test (HCT) or high-altitude simulation test (HAST). It is also sometimes referred to as a "fitness to fly" test or pre-flight oxygen test.
Purpose
The test helps doctors determine if a person with a pre-existing heart or lung condition will need supplemental oxygen while flying. Commercial airplane cabins are pressurized to a maximum altitude of 8,000 feet, which means the air has less oxygen than at sea level.
Procedure
During the HCT:

The patient rests and breathes a special gas mixture containing a reduced oxygen concentration (typically 15% oxygen, simulating the cabin environment) through a face mask or mouthpiece for up to 20-30 minutes.
A healthcare professional continuously monitors the patient's blood oxygen saturation and heart rate using a pulse oximeter clipped to a finger or earlobe.
If the oxygen levels drop below a certain threshold (e.g., 85-90% saturation, or a specific arterial oxygen partial pressure value), supplemental oxygen is administered to determine the necessary flow rate for safe travel.
In some cases, a blood sample may be taken from an earlobe or wrist before and after the test to measure blood gas levels.

The results of the test are used by a doctor to complete a medical form (often called a MEDIF) that is submitted to the airline to arrange for the required in-flight oxygen.

I stopped traveling about 3 years ago, not only due to concerns about hypoxia but also concerns about DVTs, access to bathrooms, mobility limitations, etc.