feat(icons): added phi icon also used as golden-ratio (#4218)

* Added icons/phi.svg

* Added icons/phi.json

* Updated icons/phi.json

* Add use-cases to phi.json

---------

Co-authored-by: Eric Fennis <eric.fennis@gmail.com>

icons/phi.json

@@ -0,0 +1,26 @@
+{
+  "$schema": "../icon.schema.json",
+  "contributors": [
+    "whoisBugsbunny"
+  ],
+  "use-cases": [
+    "representing the golden ratio",
+    "indicating mathematical formulas",
+    "labeling scientific variables"
+  ],
+  "tags": [
+    "math",
+    "golden-ratio",
+    "symbol",
+    "greek",
+    "letter",
+    "typography",
+    "constant",
+    "flux",
+    "magnetic-flux"
+  ],
+  "categories": [
+    "math",
+    "science"
+  ]
+}

icons/phi.svg

@@ -0,0 +1,14 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <path d="M12 2v20" />
+  <circle cx="12" cy="12" r="7" />
+</svg>