First up, if you have WiFi internet access at home, check your phone settings for "WiFi Calling". This will allow your phone to make & receive calls through your WiFi connection as if it's on the cell network. This setting is available on modern iPhones & high-end Samsung Phones (typically their Galaxy S & Note series), but may be available on other phones as well.
If you see this option on your phone, but it's disabled. Contact your cell carrier about it as they may need to add VoIP / VoLTE provisions to your account (as part of the troubleshooting on their side). You will likely need to reboot your phone afterwards (to get updated network information, which should enable the WiFi calling settings).
Second option, is to call your cell carrier & inquire about a MicroCell (aka "Femtocell" or "Picocell"), which is a small-scale, low-power cell tower that connects to your internet connection that provides added cell coverage in it's vicinity. These are generally provide a 3G network, which is reasonable for calls (not so much for data usage) & the phones that can connect to the MicroCell is controlled by the owner (so you can control who gets access to it). These typically cost around $200 to purchase from your carrier's corporate stores, online or through their customer service lines. Please be aware that cell carriers generally will NOT give you one for free unless there's a valid TECHNICAL REASON (like confirmed lack of tower coverage) for it & your phone(s) don't support WiFi calling, which will require you to talk to their Tech Support Team to reach such a conclusion.
If you're on the Prepaid counterpart of a major carrier like AT&T or Verizon, you might be able to get a MicroCell... but you'll have to pay for it (as they only give them for free to post-paid / contract subscribers as a way to help retain them as customers).
If you're on a Prepaid Network Reseller like TracFone, Total Wireless & Straight Talk (to name a few)... you're pretty much out of luck on this since they will likely be forced to get in touch with network providers they're using, resulting in more headaches than what it's worth.
All the common sense stuff still applies like try to be near a window (especially if you're building is made out of metal that acts like a Faraday cage OR brick & concrete, since wireless signals have difficulty penetrating such materials), get on top of hills, ect.
Beyond that, try to make sure you have a phone that supports the latest networks (4G LTE) as newer networks tend to have better coverage by comparison. Where I currently work, I'm in a building that's a mix of metal & concrete as well as typically working in an area that has some level of EM interference. My current phone (on the 4G LTE networks) is able to maintain a reasonable cell connection (3-4 bars) while an older phone (running on the 3G networks) had problems maintaining reception (barely keeping 1-2 bars). Considering that you mentioned that you got a newer phone, you probably got this covered (as phones made in the past 3 years are on the 4G LTE networks).
You could try rebooting your phone (to force the phone to update it's connect to the network), but it's mostly a hit-or-miss & potentially a temporary deal.
The best course of action is to check with your carrier for assistance.