Philip's predecessor (Gordian III) died during the camping against Persia / Sasanian Empire in 243.
Securing his status as emperor with senate in Rome was probably the reason for the peace treaty with Persia.
So, he settled peace with Persia and returned to Rome to secure his position (as emperor) with the senate.
Right after peace treaty Philip issued coins proclaiming that he had made peace with the Persians (pax fundata cum Persis).
Philip had the honor of leading the celebrations of the one 1000th birthday of Rome in 248 AD, which according to tradition was founded on April 21, 753 BC by Romulus.
One year later in 249 Philip was succeeded by Decius.