diff --git a/src/libs/LoginUtils.js b/src/libs/LoginUtils.ts
similarity index 56%
rename from src/libs/LoginUtils.js
rename to src/libs/LoginUtils.ts
index fdf73ea236dc..2542c485d61c 100644
--- a/src/libs/LoginUtils.js
+++ b/src/libs/LoginUtils.ts
@@ -1,4 +1,3 @@
-import _ from 'underscore';
 import Str from 'expensify-common/lib/str';
 import Onyx from 'react-native-onyx';
 import {PUBLIC_DOMAINS} from 'expensify-common/lib/CONST';
@@ -6,53 +5,44 @@ import {parsePhoneNumber} from 'awesome-phonenumber';
 import CONST from '../CONST';
 import ONYXKEYS from '../ONYXKEYS';
 
-let countryCodeByIP;
+let countryCodeByIP: number;
 Onyx.connect({
     key: ONYXKEYS.COUNTRY_CODE,
-    callback: (val) => (countryCodeByIP = val || 1),
+    callback: (val) => (countryCodeByIP = val ?? 1),
 });
 
 /**
  * Remove the special chars from the phone number
- *
- * @param {String} phone
- * @return {String}
  */
-function getPhoneNumberWithoutSpecialChars(phone) {
+function getPhoneNumberWithoutSpecialChars(phone: string): string {
     return phone.replace(CONST.REGEX.SPECIAL_CHARS_WITHOUT_NEWLINE, '');
 }
 
 /**
  * Append user country code to the phone number
- *
- * @param {String} phone
- * @return {String}
  */
-function appendCountryCode(phone) {
+function appendCountryCode(phone: string): string {
     return phone.startsWith('+') ? phone : `+${countryCodeByIP}${phone}`;
 }
 
 /**
  * Check email is public domain or not
- *
- * @param {String} email
- * @return {Boolean}
  */
-function isEmailPublicDomain(email) {
-    const emailDomain = Str.extractEmailDomain(email);
-    return _.includes(PUBLIC_DOMAINS, emailDomain.toLowerCase(), false);
+function isEmailPublicDomain(email: string): boolean {
+    const emailDomain = Str.extractEmailDomain(email).toLowerCase();
+    // That's the place where it's being checked if a general string is included in the union
+    return (PUBLIC_DOMAINS as readonly string[]).includes(emailDomain);
 }
 
 /**
  * Check if number is valid
- * @param {String} values
- * @returns {String} - Returns valid phone number formatted
+ * @returns a valid phone number formatted
  */
-function validateNumber(values) {
+function validateNumber(values: string): string {
     const parsedPhoneNumber = parsePhoneNumber(values);
 
     if (parsedPhoneNumber.possible && Str.isValidPhone(values.slice(0))) {
-        return parsedPhoneNumber.number.e164 + CONST.SMS.DOMAIN;
+        return parsedPhoneNumber.number?.e164 + CONST.SMS.DOMAIN;
     }
 
     return '';
@@ -60,11 +50,10 @@ function validateNumber(values) {
 
 /**
  * Check number is valid and attach country code
- * @param {String} partnerUserID
- * @returns {String} - Returns valid phone number with country code
+ * @returns a valid phone number with country code
  */
-function getPhoneLogin(partnerUserID) {
-    if (_.isEmpty(partnerUserID)) {
+function getPhoneLogin(partnerUserID: string): string {
+    if (partnerUserID.length === 0) {
         return '';
     }