validateToken_getUserInfo.js

//Add this code inside your Intent Handler
if (handlerInput.requestEnvelope.context.System.user.accessToken !== undefined) {

    accessToken = handlerInput.requestEnvelope.context.System.user.accessToken;

    try {
        var tokenOptions = buildHttpGetOptions(accessToken);

        var response = await httpGet(tokenOptions);
        console.log({ response });
        if (response.phone_number.length > 0) {
            phoneNumber = response.phone_number;
            const sessionAttributes = attributesManager.getSessionAttributes();
            sessionAttributes.phoneNumber = phoneNumber;

        }

    }
    catch (error) {
        console.log(`Error message: ${error.message}`);
    }
}

//Helper Function for calling the Cognito /oauth2/userInfo to get user info using the accesstoken
var https = require('https');
// https is a default part of Node.JS.  Read the developer doc:  https://nodejs.org/api/https.html
function buildHttpGetOptions(accessToken) {
    return {
        //Replace the host with your cognito user pool domain 
        host: 'accountlinkingdemo.auth.ap-south-1.amazoncognito.com',
        port: 443,
        path: '/oauth2/userInfo',
        method: 'GET',
        headers: {
            'authorization': 'Bearer ' + accessToken
        }
    };
}

function httpGet(options) {
    return new Promise(((resolve, reject) => {
        var request = https.request(options, (response) => {
            response.setEncoding('utf8');
            let returnData = '';

            if (response.statusCode < 200 || response.statusCode >= 300) {
                return reject(new Error(`${response.statusCode}: ${response.req.getHeader('host')} ${response.req.path}`));
            }

            response.on('data', (chunk) => {
                returnData += chunk;
            });

            response.on('end', () => {
                console.log({ returnData });
                resolve(JSON.parse(returnData));
            });

            response.on('error', (error) => {
                reject(error);
            });
        });
        request.end();
    }));
}