A mobile phone or cell phone can be hacked in several ways, here are some widely used methods:
Through SMS or text messages: This is the most widely used and most popular method of phone hacking. In this method, the target gets a text message with hidden payload or malicious URL and the user unknowingly grants access to hackers by clicking on the link provided in the text message.
Hacking phone using phone number: Smartphones can be hacked using phone numbers only but due to the level of difficulty and technicalities its not possible for the average person to hack the phone using this method. SS7 singling is used to connect cellphone networking with one another. Using this method hackers can record calls, forward calls, read messages, and can even get GPS location.
Hacking software: There are a number of phone monitoring software and phone spy apps available on the internet which a hacker can use to monitor your smartphone. Most such apps can be installed on the target device only with physical access but not all the hackers need physical access to the target device to install a spy app on the target phone.
Phishing: Phishing is another method used by hired hackers where they create a web page impersonating trusted companies or individuals to steal required/confidential data. In most cases, hackers gain credentials, personal information, or banking information by this method which can be later used to hack a phone or bank account.
Bluetooth hacking: Hackers can use BlueTooth as well to gain information from your cell phone, this majorly happens in public places like cafes, libraries, and hotels. Some time ago ethical hackers found a backdoor on Android 9 and older versions of android where hackers were able to connect to the device without authorization and obtain data from the target device.
Hackers can even trick you to pair your phone to their device by giving it a different name like AirPods or cafe music player which in turn can grant full access of your phone to the hacker.
Free or Open WiFi Networks: Hackers can see all unencrypted data on unsecured or open WiFi networks. Hackers set up such open networks in cafes to gain personal information, credentials, and banking information.