lodging in Koblenz, Germany-charging I-phone and tablet-& taxi/uber service

You will need a "type C" adaptor. That will work everywhere in continental Europe.

Like this one: https://store.ricksteves.com/products/european-power-adapter?variant=46194368774300

Trierer hof appears to be three blocks away from the "Koblenz Stadtmitte" station. So I would probably walk. If you get off the train at "Koblenz Hbf" there are going to be taxis. Uber exists in some parts of Germany (don't know about Koblenz) but you will end up in a taxi anyway. So maybe not deal with the company that tries to squeeze the taxi drivers dry...

For "a few days prior to the departure date," have you considered alternatives to Koblenz? Koblenz is a place that works for Rick when he books group travel, but I've found it one of the less interesting places when compared side by side with several nearby places where you might base yourself for a few days.

One go-to place on the Rhine River is Boppard, just 15 minutes south of Koblenz. It's one of the larger "old-world" towns along the Rhine with half-timbered buildings and is surrounded by vineyards, other old-world villages, and some dramatic river scenery. It's also a good place to be if you are planning to take a Rhine River Day Cruise through the scenic Rhine Gorge which lies just to the south. Boppard provides all guests with a free transport pass as well, which allows you to make train trips along the river to neighbor-towns like Bacharach, Oberwesel and St. Goar. And the same pass can be used to ride the train into Koblenz - and a bus to the Sander Hotel from there, where you presumably are staying with your group.

Boppard wine garden: https://www.deutschlandgourmet.info/bilder/gross/5710-Restaurant-Weinhaus-Heilig-Grab-Boppard.jpg

Boppard chair lift: https://www.tripadvisor.com/Attraction_Review-g198627-d3306006-Reviews-Sesselbahn_in_Boppard-Boppard_Rhineland_Palatinate.html

Bacharach:

https://en.wikipedia.org/wiki/Bacharach#/media/File:Bacharach_from_the_Postenturm.jpg

https://d3dqioy2sca31t.cloudfront.net/Projects/cms/production/000/018/452/article/720817b02d06eec7c346506f17a76585/germany-bacharach-street-100115-rs.jpg

Rhine Cruise: https://dynamic-media-cdn.tripadvisor.com/media/photo-o/17/37/65/8b/glide-down-the-river.jpg?w=1400&h=-1&s=1

Your tour does not cover this must-see area, which has been designated a UNESCO World Heritage site for good reasons.

Rebecca, Google Maps will show you precisely where anything is. Some years ago, we could not find a hotel that pleased us in Koblenz, and we stayed at a family-owned hotel in German-tourist oriented Andernach. I'm not saying that will please you, but as an example of other reasonable places that have dozens of trains a day to Koblenz, just, say, 20 minutes away.

https://community.ricksteves.com/travel-forum/transportation/kd-rhine-stop-north-of-koblenz

I like Boppard as well.

If you use Rick's or any other Type C adapter you still need your US charger to plug into it. Or, you can get a charger that has a Type C for the outlet and a USB to connect to your devices. I carry both just in case and so I can charge two devices at once. Though not as common as US hotels you may find USB outlets in your hotel.

Next to the Trierer Hof is the theatre with a big construction and at a loud intersection. Hotel Sander seems to be in a quieter area.

Main Train Station Koblenz - outside most of time taxis waiting for passengers. A big bus station, too.
Bus stop for Sanders Hotel could be „ Forum Mittelrhein Koblenz Zentralplatz 2, 56068 Koblenz“