Phoneum, or PHT, is the native ERC20 cryptocurrency of the mobile app developer by the same name. It can be earned through their games or, in this case, cloud mined via the Cloud Earning PHT app (referral link).
My favorite feature here is that the app works for a week at a time with no input from the user. Few things turn me off of a cloud mining service faster than having to check on it every hour or so, although there are a small handful like that which I am testing out. $20 buys you one year of mining at double speed. Whether that is a worthy investment depends entirely upon the fate of PHT in the future. I paid it, but it's not necessary.
One interesting thing about Phoneum is that the amount you have is shared across several of their apps, allowing you to earn in one and spend in another without having to make any withdrawals or deposits first. So, you can use this app to mine and spend that PHT directly in the games without having to wait until you reach the minimum withdrawal amount. Pretty handy.
For now, the primary function of PHT as I see it is to purchase "blockchain chests" in Crypto Treasures, which gives you tiny amounts of various cryptocurrencies currently supported by the Phoneum line of games. The games are mildly entertaining and allow beginners in crypto to examine a variety of currencies without having to invest, so I like them. Actually, Phoneum is what got me back to being interested in crypto after years of stupidly ignoring it.
I have made one successful withdrawal from this app so far. It's not exactly a gold mine, but I'm hoping to see Phoneum gain popularity as the crypto market worms its way into the mainstream over the next few years. Whatever happens, I see no reason to ignore any free crypto, regardless of market value, escpecially if you only have to tap a button once a week to get it.