[Prime] Linsoul KiwiEars Allegro "Mini" Portable 32bit/384kHz DAC, USB-C to 3.5/4.4mm $30.01 Delivered @ Linsoul via Amazon AU

was $37.99 on sale, now $30.01.

if you need something with slightly more power than Apple USB-C to 3.5mm adapter, which is highly recommended for most use cases.
to save you from searching Apple USB-C dongle currently $9 C&C at HarveyNorman and $15 on Amazon AU.

Allegro has both 3.5mm and balanced 4.4mm outputs.

Apple USB-C to 3.5mm: 31mW combined (15mW + 15mW @ 33ohm), 0.9ohm output impedance.
Kiwi Ears Allegro Mini: 60mW combined (30mW + 30mW), (balanced 4.4mm - they don't provide the info but you could estimate from Allegro Pro's 70mW 3.5mm and 155mW balanced 4.4mm, but it could be the same 60mW just with a 4.4mm connection), <1ohm output impedance.

Allegro also has very low output impedance claimed <1ohm makes it ideal for IEM's and low impedance headphones.

38 x 10 x 15 mm size. should just attach to bottom of the phone, should have enough clearance for your case but ymmv (depends on case).
modern Apple phones use USB-C are also compatible.
Google AI says additional "lightning to USB-C OTG cable required" key word being lightning.
Kiwi Ears says "USB Type-C works with in Windows, Mac, Android and iOS."

for the geeks:

• THD+N​: < 0.004% (32Ω load, A-weighted)
• Output Power​: L+R ≥ 30mW + 30mW (32Ω, THD+N < 1%)
• SNR​: ≥ 114dB (32Ω load, A-weighted)
• Frequency Response​: ±0.2dB (20-20KHz)
• Background Noise​: < 3μV (A-weighted)
• Supported Formats​: PCM (up to 32bit/384kHz),
• DSD (DSD128, DSD64)
• Output​: USB C to 3.5/4.4mm

Original Coupon Deal