Or you can eschew the phone entirely and go with a soft phone. As the name implies, a soft phone is entirely software based and resides on the PC of the user. A headset is used instead of a handset and dialing is done on the keyboard.
Why choose one over the other? Well, just as some people prefer books to Kindles, some people prefer to use an actual phone. They like the telephone keypad (which is opposite to a computer keypad in layout) and they are used to the other features of the phone being on the phone itself.
However, if your job is primarily taking or making calls then maybe a soft phone is the way to go. If the PBX is linked to the company database and can bring up customer records on the screen for incoming calls or can dial customers telephone numbers from within the application, then a soft phone has advantages.
Also, the upfront and ongoing maintenance costs of a soft phone typically are less than a hard phone. On the other hand, a soft phone lives and dies with the host PC it is running on. If you have network problems or your PC needs to be rebooted, then you cannot make or receive calls until the network issue is resolved.
Just like any technology, there is a right and wrong application for everything. One size does not fit all. Analyze your needs by employee function and make purchasing decisions accordingly.
And remember, initial cost is not the only factor to consider. Look at the total cost of ownership over the reasonable life of the system.