The PHB only gives starting wealth for Level 1 PCs. Based on my experience in other games, specifically Pathfinder, I would expect to get more at higher levels. Where can I find an appropriate table or calculation?
Starting Equipment at higher levels
Page 38 of the DMG provides a table for starting wealth and equipment at various levels.
There is a table is on page 38 of the Dungeon Master's Guide. However, the text says:
Starting equipment for characters above 1st level is entirely at your discretion, since you give out treasure at your own pace. That said, you can use the Starting Equipment table as a guide.
The table is divided into four tiers of levels (matching the tiers described earlier in the DMG). Levels 1-4 get normal starting equipment. Higher levels get that plus some gold, with a base amount plus a die-roll for a little bit more. Characters starting at levels 5-10 get 500gp + 1d10×25, 11-16 get 5000gp + 1d10×250, and 17-20 get 20,000gp + 1d10×250.
There are also columns for "Low Magic", "Standard", and "High Magic" campaigns. The table suggests that characters starting at higher tiers start with a number of items accordingly. For a "Standard Campaign", this is two uncommon items at 11th level, plus a rare one at 16th. The difference between "Low Magic" and "High Magic" at high levels is pretty stark, as the former only gets two uncommon items while the latter gets some rare ones as well — this could be as much as 60,000gp! I think it's pretty clear that when starting at high levels, especially in a "High Magic" campaign, the selection of these items should be a collaboration between the DM and player.
Also note that this section is in the context of starting a campaign at higher levels:
Experienced players familiar with the capabilities of the character classes and impatient for more significant adventures might welcome the idea of starting a campaign with characters above 1st level.
This is important because I don't think following this table blindly is the best guidance in other scenarios. For example, in After a TPK, we are re-doing the adventure at 2nd-level. Are there any guidelines for what the items and equipment the PCs should have?, it seems completely reasonable to give the new starting party basically what they had before — unless the group really likes the more hardcore "you die, you build up from scratch" approach. Or, if you have a higher level group and are bringing in a fresh player, I think giving them gear and wealth on par with the existing party makes sense — and is perfectly in line with the quote from the beginning of this answer: give the new player stuff as if they were at the same place you gave it to everyone else.
Additionally, this is not an "expected wealth by level" table as in 3.0/3.5E (and Pathfinder). Those games are explicitly designed with the expectation that this wealth is necessary to match the power curve of the game. 5th Edition takes a very different approach, with "bounded accuracy" as a core design principle. This makes magic items less of a big deal — they don't provide huge bonuses, and for example a +3 weapon is not just rare but very rare. In older editions (and explicitly so in 4E), having a +5 flaming sword is basically keeping up with the Jonses (or perhaps the Dzhoh'n'zes, in a generic fantasy setting). In 5E, these magic item bonuses aren't required by the basic game math.