Pha is the twenty-second consonant of the varnamala, the voiceless aspirated labial and the second member of the fifth varga. Like tha in the dental class, its usual romanisation misleads an English reader, who sees a letter pair that spells an f in English words of Greek origin. The Sanskrit sound is a p released with breath, and classical Sanskrit has no f at all. The scholarly transliteration systems mark aspiration with a following h precisely because they are marking a feature rather than spelling an English sound, and a reader who knows the convention can reconstruct the Devanagari letter from the Latin without ambiguity.
Modern Hindi and the other languages written with Devanagari do have an f, borrowed with vocabulary from Persian and Arabic, and they write it with this letter and a nukta dot beneath. That is one of several such dotted letters added to the script after the classical period for sounds the varnamala had no place for. Whether the dots are written at all varies by publisher and by speaker, since many speakers do not distinguish the borrowed sound from the native one, and Hindi orthography has been argued over on exactly this point for a century.
The Unicode Standard encodes both a combining nukta and a precomposed character for the dotted form of this letter, so the same Hindi word can be represented in two different sequences of codepoints. Software that compares or searches text has to normalise between them first, and a search that does not will fail to match a word against itself.