App not showing up in app store search result I am trying to download this app in samsung galaxy s4 with android 5.0.1  

I have tried looking for it in another phone with android 4.2 but it doesn't show up when I search for it in the playstore (even though the search box autocomplete shows me the exact name of the app when typing the first few letters). I assumed this was because the app says it's for Android 4.4 and up so I tried the samsung phone with Android 5.0.1 but the problem is still same. In both phones the search results are similar, but neither one of them shows me the one I want  

Why is this happening? The two phones are signed into app store through different google accounts. Is there any way to go directly to the page for this app using the Play Store app, instead of searching for it? I cannot do this through the browser because I don't have the google password for the Android 5.0.1 phone.
It's because the app is not compatible with your device, and thus Google Play Store app filters those out because the user won't be able to install from it anyway (APK sideloading is always possible though).
As stated in Android Developer's official documentation,

How filters work on Google Play
Google Play uses the filter restrictions described below to determine whether to show your application to a user who is browsing or searching for applications from the Google Play app.
When determining whether to display your app, Google Play checks the device's hardware and software requirement, as well as its carrier, location, and other characteristics. It then compares those against the restrictions and dependencies expressed by the application's manifest file and publishing details.
If the application is compatible with the device according to the filter rules, Google Play displays the application to the user. Otherwise, Google Play hides your application from search results and category browsing, even if a user specifically requests the app by clicking a deep link that points directly to the app's ID within Google Play.
(Emphasis mine)

Note that app developer can also exclude individual device model manually.

Exclude your app from certain devices
Manage excluded devices per app
To prevent app crashes, you can exclude your app from being available to individual devices on Google Play. Making this change manually excludes your whole app—you can't exclude individual APKs.
By manually excluding devices with known compatibility issues, you can help provide a better experience for your users.


For this specific case, NextRadio Free Live FM Radio depends on the FM receiver chip on the user's device. The update since January 2, 2019 also states that it doesn't support streaming anymore and only use FM-radio.

WHAT'S NEW
NextRadio is going back to basics. Streaming is no longer supported, but you can still tune to your favorite local stations on FM-enabled devices.

On the other hand, Samsung Galaxy S4 doesn't have FM radio, and it will be pointless to install the app since it won't work properly. Note that the user can always sideload the APK if they want.