Take it from this "Pekeng Pinoy"! Actually it's either PhP 1 million, 1 million PhP, 1 million pesos or just PhP1,000,000.00, either with the PhP in front or at the end!
The other expression for Piso is; isang piso, dalawang piso, tatlong piso, isang daan piso, isang libong piso and so on, but the word Piso or Peso(s) really depends on how it is used in a Tagalog or English sentence. Also an s added to the end of the word Piso is never done! Now you know when the letter s is used! It's often in Pesos (more than one coin) depending how it's used in a sentence in Tagalog or English! Confusing is it? That's MHO the way it's used coming from this "Pekeng Pinoy"!
In English though, it would be; one peso(a single peso coin), two pesos, three pesos and so on! That's how I learned it over the years just by the sound of it in Spanish, Tagalog and or in an English sentence, but I'm sure an expert linguist will disagree with me or not!