Struggling to Optimize My Country Codes Directory Online Utility for Better SEO Rankings: Any Pointers?

Hello everyone, I'm new here and a complete noob when it comes to SEO, so please bear with me! I've built a web tool called 'Country Codes Directory: International Phone, Calling, Dialing & ISO Codes'. My main goal is to get this online utility ranking higher on Google and bring in more organic traffic. Currently feeling overwhelmed and unsure how to tackle SEO for such a specific data-heavy site.

Despite having unique, accurate data, we're barely showing up for crucial keywords like "international calling codes" or "ISO country codes". Google Search Console shows very low impressions and clicks, even for long-tail queries. I suspect there's a fundamental issue with how I've structured content or handled technical SEO for this directory. I've included a simulated 'Google Search Console Performance Report' snippet below to illustrate the poor performance for some key terms:

Google Search Console Performance - Last 28 days (Simulated)

Query                     Impressions   Clicks   Avg. Position
-------------------------------------------------------------
international calling codes     150       2       87.4
ISO country codes                90       0       92.1
dialing code for germany         30       1       65.9
country codes directory           5       0       --

I've tried some basic on-page SEO, ensuring unique meta titles and descriptions for each country page. I also attempted content expansion by adding some introductory text and usage examples on country pages. For technical basics, I submitted sitemaps, checked robots.txt, and ensured mobile-friendliness. I've also tried to keep page load times reasonable for speed optimization. Unfortunately, none of these efforts seem to have significantly moved the needle.

I'm really hoping someone experienced in SEO for web applications or data directories can shed some light on this. Specifically, I'm wondering:

• What are the best SEO strategies specifically for a comprehensive online directory like a country codes list?
• How can I improve my internal linking structure to pass more "link juice" and improve discoverability of individual country pages?
• Are there any specific technical SEO considerations for a site with thousands of similar data points (e.g., country codes)?
• Should I be focusing more on schema markup for this type of data? If so, what kind?
• Any advice on how to get Google to properly index and rank all the individual country pages more effectively?

Help a brother out please...