Writing a google sheets function to only apply to changed rows - google-sheets

Question

I've recently integrated Twilio with one of my sheets to automatically send messages to phone numbers. An example process is below...
Spreadsheet contains several hundred rows with specific message details in each that twilio sends to a specific phone number
Function is set to trigger on sheet edit
User enters a phone number in rows 3, 59, and 148 that have the unique message details to send
Function triggers and sends messages
The problem is that the function I have will search the entire sheet for a phone number. I would like to write the function so it immediately knows which cells have been edited (with the new phone number) and only runs the function on those rows. So instead of taking 30 minutes to comb through every row looking for a phone number, it only looks at those rows that changed.
Any idea how I can make this happen? The function I have so far is below. I know the line I need to change, but just dont know the code to put.
function sendSms(to, body) {
var messages_url = "INSERT TWILIO URL HERE";
var payload = {
"To": to,
"Body" : body,
"From" : "[phone]"
};
var options = {
"method" : "post",
"payload" : payload
};
options.headers = {
"Authorization" : "Basic " + Utilities.base64Encode("PRIVATE INFO")
};
UrlFetchApp.fetch(messages_url, options);
}
function sendAll() {
var sheet = SpreadsheetApp.getActiveSheet();
var startRow = 2;
var numRows = sheet.getLastRow() - 1;
var dataRange = sheet.getRange(startRow, 1, numRows, 2)
var data = dataRange.getValues();
for (i in data) {
var row = data[i];
try {
response_data = sendSms(row[0], row[1]);
status = "sent";
} catch(err) {
Logger.log(err);
status = "error";
}
sheet.getRange(startRow + Number(i), 3).setValue(status);
}
}
function myFunction() {
sendAll();
}