Looking on the internet deeply has found these results:

of a high priority is the most popular phrase on the web.

of high priority 111,100,000 results on the web	of a high priority 114,300,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Where Parliament is concerned, we have used our Budget guidelines in order very clearly to designate this area as being one of high priority. It shall be a matter of high priority to put in place or appoint such a correspondent for terrorism matters. The idea of European strategy documents should be pursued as a matter of high priority. Improving road safety is a matter of high priority for Europe. In more general terms, further market access to China remains of high priority. I am pleased to report that the European Council, seeing the potential for expansion in this area, agreed that the draft directive on services, currently under consideration in the Council, should be agreed as a matter of high priority. This should be a matter of high priority, with a view to bringing about some prompt changes. Devoting resources to getting more food to a given area is therefore of high priority.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

of high priority

111,100,000 results on the web

of a high priority

114,300,000 results on the web

More popular!

Where Parliament is concerned, we have used our Budget guidelines in order very clearly to designate this area as being one of high priority.
It shall be a matter of high priority to put in place or appoint such a correspondent for terrorism matters.
The idea of European strategy documents should be pursued as a matter of high priority.
Improving road safety is a matter of high priority for Europe.
In more general terms, further market access to China remains of high priority.
I am pleased to report that the European Council, seeing the potential for expansion in this area, agreed that the draft directive on services, currently under consideration in the Council, should be agreed as a matter of high priority.
This should be a matter of high priority, with a view to bringing about some prompt changes.
Devoting resources to getting more food to a given area is therefore of high priority.

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.