How do I enable Intelephense for my Neovim config?

Question

I have a Neovim config that i use for C/C++, Python, Assembly, Rust and PHP, and in all of those the LSP's are working - highlights, coloring, autocomplete, all the things - except in Asm and PHP. I won't bother with Asm for now since I expect that to be a mountain of headaches, but why's Intelephense not working?

I installed Intelephense both with Mason.nvim and with npm, but neither are working. So, here's my Lua:

-- lsp.lua
local lsp_zero = require('lsp-zero')

lsp_zero.on_attach(function(client, bufnr)
    -- see :help lsp-zero-keybindings
    -- to learn the available actions
    lsp_zero.default_keymaps({buffer = bufnr})
end)

-- here you can setup the language servers 
require("mason").setup()

require('lspconfig').clangd.setup({}) -- C/C++ LSP
require('lspconfig').lua_ls.setup({}) -- Lua LSP
require('lspconfig').pylsp.setup({}) -- Python LSP
require('lspconfig').tsserver.setup({}) -- Javascript/Typescript LSP
require('lspconfig').html.setup({}) -- HTML LSP
require('lspconfig').cssls.setup({}) -- CSS LSP
require('lspconfig').intelephense.setup({}) -- PHP Intelephense please work

-- Autocompletion
local cmp = require('cmp')
local cmp_action = require('lsp-zero').cmp_action()

cmp.setup({
    mapping = cmp.mapping.preset.insert({
        -- `Tab` key to confirm completion
        ['<Tab>'] = cmp.mapping.confirm({select = false}),

        -- Ctrl+Space to trigger completion menu
        ['<C-Space>'] = cmp.mapping.complete(),

        -- Navigate between snippet placeholder
        ['<C-f>'] = cmp_action.luasnip_jump_forward(),
        ['<C-b>'] = cmp_action.luasnip_jump_backward(),

        -- Scroll up and down in the completion documentation
        ['<C-u>'] = cmp.mapping.scroll_docs(-4),
        ['<C-d>'] = cmp.mapping.scroll_docs(4),
    })
})

-- packer.lua
vim.cmd [[packadd packer.nvim]]

return require("packer").startup(function(use)
    use "wbthomason/packer.nvim" -- packer self-import

    use {
        'nvim-telescope/telescope.nvim', tag = '0.1.5',
        -- or                            , branch = '0.1.x',
        requires = { {'nvim-lua/plenary.nvim'} }
    } -- fuzzy finder

    use {
        'nvim-lualine/lualine.nvim',
        requires = { 'nvim-tree/nvim-web-devicons', opt = true }
    } -- lualine

    use({
        "folke/tokyonight.nvim",
        config = function()
            vim.cmd("colorscheme tokyonight")
        end
    }) -- tokyonight

    use {
        'nvim-treesitter/nvim-treesitter',
        run = function()
            local ts_update = require('nvim-treesitter.install').update({ with_sync = true })
            ts_update()
        end
    } -- treesitter

    use("mbbill/undotree") -- undotree

    use("theprimeagen/harpoon") -- harpoon

    use("CRAG666/code_runner.nvim") -- coderunner

    use {
        'VonHeikemen/lsp-zero.nvim',
        branch = 'v3.x',
        requires = {
            --- Uncomment the two plugins below if you want to manage the language servers from neovim
            {'williamboman/mason.nvim'},
            {'williamboman/mason-lspconfig.nvim'},

            -- LSP Support
            {'neovim/nvim-lspconfig'},
            -- Autocompletion
            {'hrsh7th/nvim-cmp'},
            {'hrsh7th/cmp-nvim-lsp'},
            {'L3MON4D3/LuaSnip'},
        }
    } -- LSP
end)

Here's a picture of the LSP not working as intended: