Is it this part of the code I need to change:
No. The calibration code is not printing the incorrect data.
getPh();
This is crap. A function with get in it's name should return a value. It should NOT print the value to the serial port.
pHserial.readBytesUntil(13,inputBuffer,20);//this reads back the results into the inputBuffer we created until it sees
This function returns the number of bytes it wrote to the buffer. Why are you discarding that value? You need it to make a string (a NULL terminated array of chars) from inputBuffer (an array of chars that is NOT null terminated).
Serial.print(inputBuffer);// print the pH value to the Serial port, which is connected to the LCD.
This function expects a string. inputBuffer is NOT a string.
You need to get the number of characters that readBytesUntil actually read, and then you need to stuff a NULL into the array at that position.
int cc = pHserial.readBytesUntil('\n', inputBuffer, 20); // Notice the spaces to make this more readable
if(cc < 20)
inputBuffer[cc] = '\0'; // Add the NULL
Serial.print(inputBuffer); // Viola, no more garage
Serial.print(" "); // blank any characters printed last time that were not overwritten