What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What PHP Array is
A PHP array literal: an outer array of rows, each an associative array keyed by column name.
PHP applications that need a lookup table in code rather than in a database.
What changes when you convert Excel to PHP Array
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
Values are single-quoted with backslashes and quotes escaped, so the output can be pasted into a file as is.
What carries over from Excel to PHP Array
Excel records 2 things about a table that PHP has no way to hold.
PHP has no header row. The column names are repeated as keys on every record instead, which is why the result is bigger on disk than the table it came from.
Anything visual in the Excel - weight, alignment, colour, column widths - has no counterpart in PHP and is dropped. The values are what survives.
Both formats record types, so numbers, booleans and nulls survive as themselves rather than as text.