Not from what i know, if by 'hacker' you mean a person, or a group it would be nearly impossible, they could even do what the people above said but if you just a normal person why someone would do that much effort to listen to your useless communications ? If you talk about a three letter gov agency then it may be possible to do that but not only using your phone signal, here it may be how they can do it:

1.Malware can installed in various ways, including fake software updates, emails with fake attachments, and security flaws in popular software. Sometimes the surveillance suite is installed after the target accepts installation of a fake update to commonly used software. One example i'm aware of is FinFisher, also known as FinSpy.

2.Hacking to your PC and then install an spyware on your phone when you connect it via USB or maybe even by just being in the same wireless network.

3.Just force your phone provider like AT&T or Verizon to just hang out your data, some paranoid people even believe they already have backdoor installed on their system so the gov can just spy anyone without even talking to the phone provider or your ISP, this may be true or not.

Remember that even your apps and sites your visit on your phone can track you using cookies,browser fingerprint.(I recommend using Ghostery app browser for visiting sites) Now here how to protect you against that:

1.Ignore all updates of programs you use, if you want to upgrade them do it only in their official websites using HTTPS if you can.

2.Never open attachments you receive by email, even if it looks like its from Google,or Windows

3.A security flaw in Apple's iTunes allowed unauthorized third parties to use iTunes online update procedures to install unauthorized programs, that seems to be patched but it's best to not let any app to auto-sync to your phone.

4.Only install apps from Google play store or from sources you can trust and NEVER let checked the option Unknown Fonts(may be look different on your device, mine is not in english so i'm doing a translate here)

5.Always check your apps permissions,if an notepad like app wants to send SMS or do calls then you should be very suspicious about it.

Is your phone rooted? Don't seems that way, but if you are really concerned i think you should root it because then you can harder android by that ways:

1.When you root, you usually install a superuser manager that prevents apps from gaining root access without you know, that may prevent someone from unloading something in your phone that can root it without you know and then your phone will be in their hands.

2.You can download F-Droid app from https://f-droid.org , it is like an google play of open-source apps only, and its also an open source app, so there is no hidden code that you can't check yourself, then you can download here AdAway(it blocks ads on your phone possible avoiding them to track you and you can also download additional hosts to it) You can download Android IMSI-Catcher Detect, an app that tries to detect fake base stations in GSM/UMTS Networks.(however be aware that it can fail to detect surveillance, but is better than nothing right?) You can also safely download Orbot(tor browser for android) here You can also download here AFWALL+ an firewall from your android so you can block apps to use internet You can also download NoUSSD(Ussd codes are numbers that can provide system info and even do a factory reset, and many android phones have an security flaw where they will auto dial any number touched on a web page) You can also download OS Monitor, it is an app that can see and show you all the apps and system apps that are connecting to internet, their ip's and their location on Map, the ultimate anti-spyware tool, if you see an app is always talking with an server on China for an example you should be very suspicious and use your firewall to block it. And the best, is all open-source and free!

3.Encrypt your sd-card and your device(if you encrypt your device you need to type an password everytime it boots and if you forget it you are fucked, also please make sure you use a strong password you can use https://www.grc.com/haystack.htm#top to help you plan it)

4.Use an VPN that complety don't log anything and can even be paid in bitcoin, use google to search and also search for reviews for it,read where they operate and their ToS

5.The ultimate and paranoid solution,consider buying a 'dumb but safe' phone like the old nokias phones for you more sensitives requirements, remove your battery if you are with your device near and having sensitive talk with someone, and even consider buying many phones for 1 use only with pre-paid chips, pay them with money only

Thats all i remember for now, hope it helps!