One reason I have an iPhone, is it's extremely rare, almost unlikely you can put an app on your phone that has spyware or malware in it.  However, a lot of people have Android phones, so you're at more risk.  If you have an Android phone, according to lifehacker.com, you could be at high risk for malware, especially if you have certain apps on your phone.

According to Mike Epstein at Lifehacker, you should check your phone for the following apps.

Snow Heavy Excavator Simulator

Hoverboard Racing

Real Tractor Farming Simulator

Ambulance Rescue Driving

Heavy Mountain Bus Simulator 2018

Fire Truck Emergency Driver

Farming Tractor Real Harvest Simulator

Car Parking Challenge

Speed Boat Jet Ski Racing

Water Surfing Car Stunt

Offroad Wood Transport Truck Driver 2018

Volumen booster & Equalizer

Prado Parking Adventure

Oil Tanker Transport Truck Driver

Have any of these apps?  There are specific step to take to safely remove them.  Follow the instructions from lifehacker.

Some of these apps are creating backdoor hacks into your phone that could potentially expose more personal info about you, credit card info, personal pictures(even the sketchy hidden ones.

Also, it's a good idea on an Android phone to make sure you have some sort of malware or virus scanning program(yet another thing you don't need on an iPhone).

If you have an Android phone and you have these apps, have a fun weekend cleaning up your phone :)