Girl:
Phaene
Phaeo
Pharailde
Phedora
Phèdre (or Phaedra)
Pheobe
Pherusa
Phesyle
Philadelphia
Philaminte
Philby
Philiberte
Philine
Philipotte
Philippine
Philomela
Philomena
Phthonia
Phyllida
Phyllis
Phyllodoce
Boy:
Phaedo
Pharaoh
Phelan
Philemon
Philibert
Philinte
Philo
Philomelos
Philosophy
Philotheos (inversion of Theophilus)
Phineas
Phocas
Phocion
Phoebus
Phosphoros (double “ph”)
Photius
Phrixos
Phrynichus
Phyllon
Also, there’s the -ippe part of Philip that means “horse”. Other names that have this are: Alcippe, Aristippe, Chrysippus, Gylippus, Hippocrates, and Hippolyte for a boy and Aganippe, Alcippe, Cidippe, Cydippe, Dioxippe, Hipponoe, Hippothoe, Menippe, Xanthippe, and Zeuxippe for a girl.
Names that contain “ph”: Adelpha, Alphonsine, Amphinome, Amphithoe, Amphitryon, Aphelia, Aphrodite, Aphrotrite, Capheira, Daphne, Dauphine, Delphine, Dymphna, Epaphroditus, Ephyra, Epiphany, Eriphyle, Euphemia, Euphrosyne, Gustaphine, Iphigenia, Iphianassa, Iphis, Josephe, Josephine, Memphis, Nephele, Ophelia, Ophira, Orphise, Persephone, Raphaelle, Sapphira, Sappho, Seraphina, Séraphïta, Sophie, Sophronia, Stephanie, Symphony, Theophania, Theophila, Tryphosa, Zephyr, and Zephyrine for girls
Alpheus, Alphonse, Amphictyon, Amphilochus, Amraphel, Aphrodisius, Aristophanes, Arnolphe, Asaph, Bardulph, Bellerophon, Cephas, Cephus, Christopher, Dalphon, Daphnis, Elihoreph, Eosphoros, Eliphalet, Eliphaz, Epaphroditus, Ephah, Epher, Ephraim, Gandolph, Gryphus, Haphaestus, Hasupha, Humphrey, Iphitas, Japhet, Jehoshaphat, Jephunneh, Joseph, Ludolphe, Marphurius, Menulph, Metaphraste, Morpheus, Murphy, Neophytos, Nicephorus, Onesiphorus, Ophir, Orpheus, Pandolph, Porphirios, Potiphar, Ralph, Randolph, Raphael, Riphath, Seraphim, Shaphat, Sheleph, Shephatiah, Shepho, Sisyphus, Sophocles, Sophonie, Stephan, Theophilus, Theophylact, Tryphine, Xenophon, Zephaniah, Zepho, Zephyr, Ziphion, and Zophar for boys
Also, a neat inversion of the name Philip is Hippophilos.
This includes any of the variants as well. I excluded names with "f"s, but if I were to use the letter, I would use “ff” in a name. Names like Griffin or Ffiona (which I’m guessing is a variant of your friend’s name) I think work best because it does place emphasis on the double letter. And if you replace the “ff” with “ph” it keeps the balance of the name. So Griffin becomes Gryphon which has the same amount of letters. There’s also Irish and Scottish beauties that contain “bh” which makes the “f” sound.