The cable coming into my house has a capacity greater than my broadband speed, obviously so because it's quite possible to run broadband at full speed while watching TV
Copper phone wire is Cat3 twisted pair. Designed for analogue up to 0.04MHz
Coax is for up to 500MHz on really old stuff (1960s) and up to 2200MHz now, though they only use up to about 850MHz.
Also phone cable is noisy and has crosstalk to other cables in the bundles. Coax is much more noise free, allowing about 4x to 16x more data in the same data clock speed*.
Fibre has more capacity than coax. But Coax has a capacity of about 88 downstream channels each of 8MHz Each can be multiple TV channels (up to about 20 SD or 8 HD) or Modem data, each maybe 80Mbps to 160Mbps depending on noise level. Those channels can be shared to several modems. Or when a Cable distribution street cabinet is fibre fed, the cable is not shared so much and one modem can use up to 5 channels, or 400Mbps to 800Mbps of data.
On a fully digital Cable system there may be up to 60 channels dedicated to modems. The speed isn't affected by cable length.
Because phone cable was only designed for audio (analogue phone) for 900m the maximum is about 20Mbps. At 3km it might only be 2Mbps. The VDSL speeds above 22Mbps only apply on very short phone wires from a fibre fed cabinet or less than 500m from an exchange.
EDIT:
Was called away.
So one coax from fibre fed cabinet might simultaneously have 300 TV channels, mix of SD & HD, and perhaps 10,000 Mbps of data. The TV is "broadcast" so any number of setboxes (thousands easily) can be fed. If the cable is for 50 houses then simultaneous data per house is 10,000 / 50 = 200Mbps. But only some people are doing really simultaneous stuff, so in practice they can sell 240Mbps (you need less than 0.9km of phone wire to have a 1/10th of that) and even if they only dedicate 1,000Mbps of coax to data then mostly you'll get nearly 240Mbps.
In ADSL days they where allowed to provision the exchange poorly enough that contention was typically 48:1 rather than the 10:1 that cable might use. The theory being that if exchange had 500 broadband users at average 3Mbps (typical due to wire length) then instead of 500 x 3 = 1,500Mbps of data capacity for exchange they only installed 31Mbps (in practice either 2, 10, or 100). Problem is at 8pm maybe many people ARE on line, so you get a 1/4 of speed or worse than at 3am. When they upgrade exchange feed they market it as Fibre. You just get 3AM speed at 8pm, it's limited really by distance of copper twisted pair and cross talk, noise etc.
EDIT 2:
All Digital signals other than say Morse code are actually sent via coded analogue signals. The speed at which the signal changes is limited by the channel width (1.7MHz DAB, 8MHZ European cable and Terrestrial, 6MHz USA Cable and Terrestrial and 10MHz to 100MHz for Satellite). Phone wires use an adaptive channel width up to about 16MHz or more depending on length of wire, connection quality, crosstalk etc. Can be less than 1MHz as it's only designed for 0.04MHz).
If the power is higher or noise /crosstalk lower or both you can "code" more bits of data on each change. So Satellite which is really weak and noisy might have only 2 bits per change. Fibre might have 10 bits per change or more. Microwave links perhaps 4 bits and Cable Coax maybe 8 bits (longer older) to 10 bits (newer fibre cabinet).
so an 8MHz microwave link might manage 30Mbps. On a coax Cable an 8MHz channel might be nearly 100Mbps.
Then part of the data is used for Forward Error Correction (FEC). This can be 1/2 on Satellite and only 1/8th Cable. It's usually high on phone wires.
