In many accents of French, the letter "o" has two pronunciations that can be written in IPA as [o] and [ɔ]. Neither vowel is the same as the vowel in the French word la, which is transcribed in IPA as [a].
Neither vowel is the same as English "toe" either. The English word "toe" tends to be pronounced as a diphthong or gliding vowel, with a sound at the end like a "w" or short "oo" sound, while French vowels in most accents are pure and do not change from start to finish. But I think that English "toe" is a better approximation for both vowels than English "pah".
The distinction between [o] and [ɔ] is not consistent across all accents of French: different accents use one or the other sound in the same position. Most accents do use [ɔ] in words spelled with "o" followed by -mme, -nne or -tte, such as homme, bonne, grotte.
In many accents of France, the sound [ɔ] does not occur at the end of any words. In an accent like that, Po could only be pronounced [po]. But in an accent that allows [ɔ] at the end of a word, I guess Po could be pronounced [pɔ].
The distinction between [o] and [ɔ] (and likewise [e] and [ɛ], and [ø] and [œ]) in non-final syllables tends to be much less clear than the distinction in final syllables, so I don't know whether you should even bother trying to remember which words have [ɔ] vs. [o] in non-final syllables. As a non-native speaker, I remember being taught to use [ɔ] in general for "o" in non-final syllables, but I don't know how much reason there is to follow that convention. An answer to the previous question Do I have to learn /o/ or /ɔ/ separately? made the reverse recommendation (user21018's answer there says non-final open syllables tend to have [o]).