Is it possible for my Samsung S8+ to give a virus to a network just by using the WIFI? My boss told me my phone could give the network a virus if i use the wifi. Is he full of it??
It's possible, but unlikely. This question has an answer here, but the short version is that it completely depends on the type of malware.
If you have a malicious app installed on your phone - either because it slipped through the Play Store or because you installed it from an untrustworthy source - then that app could certainly attempt to compromise computers on any network the phone connects to. It's unlikely to be a virus, technically - more likely a Trojan, which is when a program does something malicious that you don't want in addition to doing the thing you do want (many pirated Android apps have these) - but any kind of malware might then try to infect other machines on the same network.
I haven't specifically heard of any Android malware that tries to spread to Windows/Mac/Linux computers via the network, but it wouldn't be hard to write one (if you had a vulnerability to try exploiting). Network attacks can come from any network-connected device, regardless of whether that device is the same type of thing as the target of the attack. Attacking the network itself is also possible; a malicious app could do things like scan the network for files that look valuable and send them to an attacker, or work on brute-forcing passwords for sensitive data, or just give an attacker a back door to run arbitrary commands behind your corporate firewall. With some way to get elevated privileges (easy on a rooted phone, and most phones have some way to root them), a malicious app could even use ARP spoofing to intercept network traffic from other users.
Your boss is being cautious, but not necessarily paranoid. Devices that the company can't control are more likely to be infected with malicious software, and getting an infected device on your company network is a Bad Thing. Depending on where you work, there might actually be people out there already looking for a way into your employer's network.