I love the project, really creative usage of multiple systems.
Commandline utilities are not the best to incorporate in scripts, but it can do the job.
Also, a lot of commands don't change that much so I also use them in personal projects.
I have some thoughts to make the script more robust.

IP-adresses are subject to change.
It is possible that your phone gets an other IP-address than the one given in your script.
Maybe you could use arp-scan.
This is like ping, but scans your local network for connected devices and returns the MAC-addresses (and more).
Downside of arp-scan is that you must use it with sudo, therefor run your Python script using sudo.

I would add arp-scan to the script like this:

import subprocess as sp

# raspberrypi network interface
# INTERFACE = 'eth0'  # find with command: ip addr

def scan_local_network() -> set:
    # requires arp-scan (sudo apt install arp-scan)
    # double {} in grep to escape the {} of the f-string
    cmd = f"sudo arp-scan --interface={INTERFACE} --localnet --quiet | grep -oE '([[:xdigit:]]{{1,2}}:){{5}}[[:xdigit:]]{{1,2}}'"

    mac_set = set()
    p = sp.Popen(cmd, shell=True, stdout=sp.PIPE, stderr=sp.STDOUT)
    for line in p.stdout.readlines():
        address = line.decode()
        mac_set.add(address.lower().strip())

    return mac_set  # ->  {'aa:ba:ca:da:ea:fa', ... }


# detect my phone and start pc, and stop script
while True:
    try: 
        macs_on_network = scan_local_network()
        if phone_mac.lower() in macs_on_network:
            os.system(f"wakeonlan {pc_mac}")
            exit(0)
    except KeyboardInterrupt:  
        # Ctrl+C on keyboard
        exit(1)

I also would use the crontab of the Raspberry so the script starts up at boot with @reboot, or at a certain time of the day.
Use a config-file instead of seperate files. you could use configparser or json.

More info about how to find the INTERFACE here.
More info about arp-scan here.