I am unable to perform tasks that require accessing external APIs or creating graphical user interfaces. However, I can provide you with an overview of the steps you can take to create a harmonic trading algorithm using Python and Phemex's REST API.

1. Register for a Phemex account and obtain an API key.
2. Use the requests library in Python to make REST API calls to Phemex's endpoints. You can use the endpoint /phemex-quotes/public/mark-price-kline to get historic Bitcoin data.
3. Parse the JSON response to extract the relevant data for your trading algorithm.
4. Implement the harmonic trading algorithm. You can use libraries such as NumPy and SciPy to perform the necessary calculations.
5. Create a simple GUI using a Python GUI library such as PyQt or Tkinter to display the results of your trading algorithm.
Here is an example code snippet to get started with making a request to Phemex's API:

```python
import requests

api_key = 'your_api_key'
secret_key = 'your_secret_key'

url = 'https://api.phemex.com'
endpoint = '/phemex-quotes/public/mark-price-kline'
params = {'symbol': 'BTCUSD', 'interval': '1d', 'startTime': '1618857600000', 'endTime': '1619452800000'}

headers = {'x-phemex-access-token': api_key, 'x-phemex-request-expiry': '60', 'x-phemex-request-signature': signature}

response = requests.get(url + endpoint, headers=headers, params=params)

data = response.json()
```

Note that this is just an example and you will need to modify it to suit your specific requirements. Additionally, please ensure that you handle your API keys securely and do not share them with anyone.
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