This design is an adjustable holder arm for phones, camera and anything else you want to attach to it based on modular links attached by ball join junctions and secured by a robust screw nut part.
The arm is designed to be strong (even a bit bulky) to provide a reliable, rigid base even at a length of 1 to 1.2 meters.

For a detailed description and instructions on building this setup step by step please look on Instructable:
https://www.instructables.com/Build-a-Robust-and-Modular-Helper-Arm/

The arm primarily attaches to a table plate using the "large" or "small" base part. However the arm and the phone and camera holders are also compatible with my magnetic and suction cup bases if you want a quick attachment method: https://www.thingiverse.com/thing:7403631    https://www.thingiverse.com/thing:7403625

On top of the arm you can chose to place the phone holder or the camera holder but you can also fix my printed vice (https://www.thingiverse.com/thing:7403644) to hold any object you want.

The phone holder exists in two versions. The standard version will work with basically all phone as long as you do not use a thick phone case for protection. Otherwise you can print the XL version. The phone case requires 2x 90mm long 3mm thick metal rods to serve as slide (the XL version requires 100mm rods). It also requires 5x 15mm long M3 bolts with 2x M3 nuts and 1x 20mm long M5 bolt with 1x M5 nut.

The camera holder requires a 1/4" 20 UNC bolt 18 to 20mm long to adapt to standard camera mount threading. It also requires a 25mm long M5 bolt with a nut.

The ball join links should be printed 3 to 5 times depending on the length you want for the arm. They print without support in the same orientation as the STL file. The nut remains captive around the ball. The top link exists in two version depending if you prefer to use melt inserts (M3 4.2mm OD, 4mm thick) or simple M3 nuts to attach the tool to the arm.
In any case you will need 8x 6 to 10mm M3 bolts to attach the arm to its base and the tool to the arm.

The tabletop base exist in two versions depending on the thickness of your table top. Base_small is adapted for tabletops up to 18mm thick while "Base_large" should work up to 30mm thick. The base part uses TPU pads to increase the friction with the tabletop and improve stability. The base parts use 4x 8 to 20mm M3 bolts to secure the various elements of the screws together.

Most parts should be printed with 0.2mm layers, 4 walls and 25% infill. The ball join links can be printed at 0.24mm layers to save on printing time. They are designed with coarse treading and still work well with relatively thick layers.