I think you can break it down further, ie the 上りpart of 上りましょう I think acts like a noun, ie “climbing”. Take 山登り (mountain climbing, pronounced やまのぼり、Japanese seems to have a thing where kun’yomi readings that are identical and have near identical meanings but different nuances have different kanji).
This is why it’s important to learn grammar and kanji at the same time, so you can see in context why they’re different. The の following the 上 in the second sentence is an attribution particle, so the ひょう I would assume is 表 and if you were reading the sentence with full kanji it would appear as 上の表 where the “above” is an attribution of the word that follows and makes it more clear that の is a particle, therefore meaning 上 is to be read as a standalone word (namely うえ).
Like if I said 机の上に、even if you don’t know the first word, the second you can read as うえ because you would know that に is a particle. Whereas if I said 山を上った、you would know that った is the plain past conjugation of a godan る verb and know it is read やまをのぼった。kanji alone is not enough.