you need to use a parser such as cheerio

then you need to read/provide data to it (the HTML), and then you can select the data you need by using its API:

const cheerio = require('cheerio');

const data = `
<Response>
<SMSMessageData>
    <Message>Sent to 1/1 Total Cost: NGN 2.2000</Message>
    <Recipients>
        <Recipient>
            <number>+9109929199111</number>
            <cost>NGN 2.2000</cost>
            <status>Success</status>
            <statusCode>101</statusCode>
            <messageId>ATXid_f615eb5c6e901459e52d67d045a55355</messageId>
            <messageParts>1</messageParts>
        </Recipient>
    </Recipients>
</SMSMessageData>
</Response>
`;


const $ = cheerio.load(data);

const num = $('number').text();

console.log(num);

Using the getElementsByTagName which will return the element with the specified tag (in your case the number tag). then you can select the first element use the innerText property to extract the text value of the element.

const el = document.getElementsByTagName('number')[0];
console.log(el.innerText);

<Response>
<SMSMessageData>
    <Message>Sent to 1/1 Total Cost: NGN 2.2000</Message>
    <Recipients>
        <Recipient>
            <number>+9109929199111</number>
            <cost>NGN 2.2000</cost>
            <status>Success</status>
            <statusCode>101</statusCode>
            <messageId>ATXid_f615eb5c6e901459e52d67d045a55355</messageId>
            <messageParts>1</messageParts>
        </Recipient>
    </Recipients>
</SMSMessageData>

To do this, simply tell the system to fetch the HTML element by calling document.querySelector("number"), and then use the innerText property to get the text content of the string. Use the code below to set a variable content to the text inside of the number tag.

var numberElement=document.querySelector("number"); //Fetch the element
var content=numberElement.innerText; //Retrieve its contents