Can I take a fully-charged portable phone charger on a plane? [duplicate]

No.

Source: https://www.iata.org/whatwedo/cargo/dgr/Documents/lithium-battery-guidance-document-2017-en.pdf

Lithium ion batteries packed by themselves (Packing Instruction 965) (not contained in or packed with equipment): (a) must be shipped at a state of charge (SoC) not exceeding 30% of their rated design capacity

Now, the battery within your power pack is contained within equipment, so to all appearances that's no issue. It's not a battery, after all, it's equipment with a battery inside.

However:

Power Bank (power pack, mobile battery, etc.). These are portable devices designed to be able to charge consumer devices such as mobile phones and tablets. For the purposes of this guidance document and the IATA Dangerous Goods Regulations, power banks are to be classified as batteries [...] For carriage by passengers, power banks are considered spare batteries [...]

So, the power bank itself is a battery. And thus, no more than 30% charge.