I have an iPad Pro 11 “ 3rd generation

Most models of iPad require a Power Adapter rated at 12W or greater to reliably charge. 5W Power Adapters intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Your iPad was likely supplied with a 20W USB-C Power Adapter.

While most iPhone Power Adapters are not sufficiently powerful to charge an iPad, all Power Adapters suitable for charging an iPad will also charge an iPhone - and in many cases, charge the iPhone much faster.

Modern iPads all have a USB-C port. By contrast, all models of iPhone (and some older models of iPad) use a Lightning connector. As such, as already highlighted by FoxFifth, you will always require the appropriate (and different) charging cable for both iPad and iPhone. So, to charge both your iPad and iPhone, you just need one suitable Power Adapter - and two cables.

Assuming that you’ll use your iPad’s 20W USB-C Power Adapter…

• USB-C Charge Cable (1m) - this being the cable that you already have:

https://store.apple.com/xc/product/MQKJ3ZM/A

And for your iPhone…

• USB-C to Lightning Cable (1m)

https://store.apple.com/uk/xc/product/MM0A3ZM/A

The iPad Pro 11" 3rd generation came with a 20 watt USB-C power adapter and a USB-C to USB-C cable. You can use that power adapter for both your iPad and your iPhone but will need to use the USB-C to Lightning cable for your iPhone (i.e., you will need to carry only one power adapter but two different cables).