Until we can establish independant colonies in Antartica and under the oceans we shouldn't even consider outer space. There are just so many technological steps that need to be accomplished first.
Nah, the thing is there’s different engineering demands on those locations, and a legal issue for Antarctica as well. - shifting ice moving at different rates on a the ice cap and even more so on glaciers, and legally we consider it a protected environment we explicitly don’t want to colonise - the oceans is corrosive, plant and animal life is everywhere from biofilms to barnacles your stuff is going to become covere…
Regarding your last suggestion, what you actually want is a skyhook to catch the payload, with Phobos at the center. You can even use Phobos regolith to manufacture the basalt fiber required to build the cable.