What you have heard is exactly correct. The difference is not reflected in spelling, however, because native speakers of English do not hear the difference. To our ears /p/ and /ph/ are the same sound.
You hear these as different sounds because your language (or one you are familiar with—Urdu, perhaps?) distinguishes aspirated stops ph,dh,th,dh,kh,gh, which have a little puff of air when the consonant is 'released', from unaspirated versions of the same sounds which do not have the puff of air—p,b,t,b,d,g.
In your language these aspirated stops are distinct phonemes—sounds which distinguish one word from another. In English, however, they are not phonemes but merely allophones—variant versions of a phoneme which occur in specific phonetic environments.
Specifically, in English the voiceless stop phonemes ( /p/,/t/,/k/ ) are pronounced as aspirate phones ( [ph],[th],[kh] ) only at the beginning of a word or stressed syllable, and then only if they are not preceded by /s/. But in these contexts the phonemes /p/, /t/, /k/ are always aspirated.
The voiced stop phonemes /b/, /d/, /g/ are not aspirated.