So, pa and pha might be allophones in a language like English, but it is not going to be considered as an allophone in Hindi because in English it could be allophones, but in Hindi it will not be because they cannot be used as a substitute to each other.
इस तरह प और फ अंग्रेजी में एलॉफोंस हो सकते हैं, हिंदी में नहीं, यहां पर ये एक दूसरे के लिए नहीं इस्तेमाल किए जा सकते।